Today, computing devices such as personal computers, laptop computers, personal digital assistants, cell-phones, etc., are routinely used at work, home, and everywhere in-between. Computing devices advantageously enable the use of application specific software, file sharing, the creation of electronic documents, and electronic communication and commerce through the Internet and other computer networks. Typically, each computing device has a storage peripheral such as a disk drive.
A huge market exists for disk drives for mass-market computing devices such as desktop computers, laptop computers, as well as small form factor (SFF) disk drives for use in mobile computing devices (e.g., personal digital assistants (PDAs), cell-phones, digital cameras, etc.). To be competitive, a disk drive should be relatively inexpensive and provide substantial capacity, rapid access to data, and reliable performance.
Disk drives typically comprise a disk and a head connected to a distal end of an actuator arm which is rotated by a pivot by a voice coil motor (VCM) to position the head radially over the disk. The disk typically comprises a plurality of radially spaced, concentric tracks for recording user data sectors and servo sectors. The servo sectors typically comprise head positioning information (e.g., a track address) which is read by the head and processed by a servo control system to control the velocity of the actuator arm as it seeks from track to track.
Data is typically written to the disk by modulating a write current in an inductive coil of the head to record magnetic transitions onto the disk surface. During readback, the magnetic transitions are sensed by a read element (e.g., a magnetoresistive element) of the head and the resulting read signal is demodulated by a suitable read channel.
Disk drives often dynamically load a head onto the disk into a load zone during start-up. For example, typically, the head is loaded off a ramp onto outer diameter (OD) tracks that may be dedicated to being a load zone. The load zone may include a plurality of outer diameter tracks that span the width of the slider of the head. The load zone is typically not used for user data because of potential data loss due to head media contact (HMC) when the head is loaded onto the disk. HMC may thermally demagnetize the disk or damage the data layer. In particular, many disk drives utilize a dynamic load/unload (LUL) process to load the heads onto the media load zone (LZ) from a ramp during start-up and unload them from the LZ during shutdown.
Although previous attempts have been made by manufacturers to utilize the LZ for data storage in order to increase disk drive capacity, these efforts have been mostly abandoned due to data corruption from the violence of the LUL process. For example, heads may strike the media during the LUL process resulting in: thermal excursions that can demagnetize the disk; or actual physical damage that can destroy the data layer and produce asperities that can grow and ultimately result in head crashes. Accordingly, techniques to effectively utilize the LZ for data storage are sought after.